1. Field of the Invention
The present invention is concerned with processing of speech signals, particularly those which have been distorted by amplitude-limiting processes such as clipping.
2. Related Art
Apart from its obvious effect on perceived speech quality, clipping in a telecommunications system is disadvantageous in that it reduces the dynamic range of the signal which can adversely affect the operation of echo cancellers. According to the present invention there is provided an apparatus for processing speech comprising: means to apply to a speech signal a wavelet transform to generate a plurality of transformed components each of which is the convolution of the signal and a respective one of a set of wavelets g(t/a.sub.i) where a.sub.i is a temporal scaling factor for that component and g(t) is a temporally finite waveform having a mean value of zero; means to modify the components; and means to apply to the modified components the inverse of the said wavelet transform, to produce an output signal; wherein the modifying means is operable to scale at least some of the components differently from one another such as to increase the dynamic range of the output signal.
Other, preferred, aspects of the invention are defined in the claims.